After much wailing and gnashing of teeth it would appear that the solution is this:
Problem: HTTPS stopped working once URL Scan 3.1 installed on XP machine running IIS5.1
Solution: Move the URL Scan ISAPI filter to below the sspifilt ISAPI Filter
Can anyone tell me if this is the *correct* solution to the problem, i.e. that there will be no unwanted side effects?
Thanks,
Patrick